With the increasing thinness and fineness of mobile products such as mobile phones and tablet computers, screen with higher resolution and smaller thickness is desired, therefore, in-cell touch display screen with simple structure has gradually become the mainstream of the development of market.
An in-cell touch display screen comprises a display panel, the display panel comprises gate lines, common electrode lines, pixel electrodes and a common electrode, wherein the common electrode lines are used as touch-control scanning signal lines in the touch-control driving circuit.
An operation cycle of the in-cell touch display screen includes a display phase and touch-control phase. In the touch-control phase, the common electrode line, as the touch-control scanning signal line in the touch-control driving circuit, is driven in a time sharing manner. In the touch-control phase, the display panel is not supplied with display signals any more, therefore, in the touch-control phase, only a voltage difference between the pixel electrodes and the common electrode is needed to maintain the angle of deflection of the liquid crystal molecules.
Since the touch-control scanning signal lines are connected to the common electrode, a voltage of the common electrode in the touch-control phase is different from that of the common electrode in the display phase, in order to maintain the angle of deflection of the liquid crystal molecules, a voltage of the pixel electrode should be changed so as to maintain the voltage difference between the pixel electrode and the common electrode. With variation of the voltage of the common electrode in the touch-control phase, the voltage of the pixel electrode also varies, however, a voltage of a gate of a thin film transistor of an existing display panel usually remains the same during the touch-control phase, which results in variation of voltage between the gate and source connected to the pixel electrode of the thin film transistor, so that a phenomenon in which a curve of the transconductance of the thin film transistor in the pixel unit is drifted always occurs after the display screen operates for a while, affecting the service life of the thin film transistor.